Method of fabricating phase change memory cell

ABSTRACT

A semiconductor device is disclosed. In one embodiment, the semiconductor device includes a memory cell, which in turn includes an electrode and a phase change material. The electrode may be disposed on a substrate and include a sublithographic lateral dimension parallel to the substrate. The phase change material may be coupled to the electrode and include a lateral dimension parallel to the substrate and greater than the sublithographic lateral dimension of the electrode. Various semiconductor devices and manufacturing methods are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/357,222,filed Jan. 21, 2009 and issued on Mar. 30, 2010 as U.S. Pat. No.7,687,881, which is a divisional of application Ser. No. 11/861,202,filed Sep. 25, 2007, and issued on Feb. 24, 2009 as U.S. Pat. No.7,494,922, which is a continuation of application Ser. No. 10/931,196,filed Aug. 31, 2004, and issued on Sep. 25, 2007 as U.S. Pat. No.7,273,809, which is a continuation of application Ser. No. 10/384,267,filed Mar. 7, 2003, and issued on Sep. 28, 2004, as U.S. Pat. No.6,797,612, which is a divisional of application Ser. No. 09/900,725,filed Jul. 6, 2001, and issued on Mar. 11, 2003, as U.S. Pat. No.6,531,391, which is a divisional of application Ser. No. 08/684,815,filed Jul. 22, 1996, and issued on Jan. 8, 2002, as U.S. Pat. No.6,337,266.

BACKGROUND OF THE INVENTION

The present invention relates generally to chalcogenide memory devicesand, more particularly, to a chalcogenide memory device having anultra-small electrode, thus providing for fabrication of a denser memoryarray and reducing the amount of energy required to adjust thecrystalline state of the chalcogenide material.

The use of electrically writable and erasable phase change materials(i.e., materials which can be electrically switched between generallyamorphous and generally crystalline states or between differentresistive states while in crystalline form) for electronic memoryapplications is known in the art and is disclosed, for example, in U.S.Pat. No. 5,296,716 to Ovshinsky et al., the disclosure of which isincorporated herein by reference. U.S. Pat. No. 5,296,716 is believed toindicate generally the state of the art, and to contain a discussion ofthe current theory of operation of chalcogenide materials.

Generally, as disclosed in the aforementioned Ovshinsky patent, suchphase change materials can be electrically switched between a firststructural state where the material is generally amorphous and a secondstructural state where the material has a generally crystalline localorder. The material may also be electrically switched between differentdetectable states of local order across the entire spectrum between thecompletely amorphous and the completely crystalline states. That is, theswitching of such materials is not required to take place betweencompletely amorphous and completely crystalline states but rather thematerial can be switched in incremental steps reflecting changes oflocal order to provide a “gray scale” represented by a multiplicity ofconditions of local order spanning the spectrum from the completelyamorphous state to the completely crystalline state.

The material exhibits different electrical characteristics dependingupon its state. For instance, in its amorphous state the materialexhibits a lower electrical conductivity than it does in its crystallinestate.

These memory cells are monolithic, homogeneous, and formed ofchalcogenide material selected from the group of Te, Se, Sb, Ni, and Ge.Such chalcogenide materials can be switched between numerouselectrically detectable conditions of varying resistivity in nanosecondtime periods with the input of picojoules of energy. The resultingmemory material is truly non-volatile and will maintain the integrity ofthe information stored by the memory cell without the need for periodicrefresh signals. Furthermore, the data integrity of the informationstored by these memory cells is not lost when power is removed from thedevice. The subject memory material is directly overwritable so that thememory cells need not be erased (set to a specified starting point) inorder to change information stored within the memory cells. Finally, thelarge dynamic range offered by the memory material provides for the grayscale storage of multiple bits of binary information in a single cell bymimicking the binary encoded information in analog form and therebystoring multiple bits of binary encoded information as a singleresistance value in a single cell.

The operation of chalcogenide memory cells requires that a region of thechalcogenide memory material, called the chalcogenide active region, besubjected to a current pulse typically with a current density betweenabout 10⁵ and 10⁷ amperes/cm², to change the crystalline state of thechalcogenide material within the active region contained within a smallpore. This current density may be accomplished by first creating a smallopening in a dielectric material which is itself deposited onto a lowerelectrode material. A second dielectric layer, typically of siliconnitride, is then deposited onto the dielectric layer and into theopening. The second dielectric layer is typically on the order of 40Angstroms thick. The chalcogenide material is then deposited over thesecond dielectric material and into the opening. An upper electrodematerial is then deposited over the chalcogenide material. Carbon is acommonly used electrode material, although other materials have alsobeen used, for example, molybdenum and titanium nitride. A conductivepath is then provided from the chalcogenide material to the lowerelectrode material by forming a pore in the second dielectric layer bythe well known process of firing. Firing involves passing an initialhigh current pulse through the structure which passes through thechalcogenide material and then provides dielectric breakdown of thesecond dielectric layer, thereby providing a conductive path via thepore through the memory cell.

Electrically firing the thin silicon nitride layer is not desirable fora high density memory product due to the high current required and thelarge amount of testing time that is required for the firing.

The active regions of the chalcogenide memory cells within the pores arebelieved to change crystalline structure in response to applied voltagepulses of a wide range of magnitudes and pulse durations. These changesin crystalline structure alter the bulk resistance of the chalcogenideactive region. The wide dynamic range of these devices, the linearity oftheir response, and lack of hysteresis provide these memory cells withmultiple bit storage capabilities.

Factors such as pore dimensions (diameter, thickness, and volume),chalcogenide composition, signal pulse duration and signal pulsewaveform shape have an effect on the magnitude of the dynamic range ofresistances, the absolute endpoint resistances of the dynamic range, andthe currents required to set the memory cells at these resistances. Forexample, relatively large pore diameters (e.g., about 1 micron) willresult in higher programming current requirements, while relativelysmall pore diameters (e.g., about 500 Angstroms) will result in lowerprogramming current requirements. The most important factor in reducingthe required programming current is the pore cross sectional area.

The energy input required to adjust the crystalline state of thechalcogenide active region of the memory cell is directly proportionalto the dimensions of the minimum lateral dimension of the pore (e.g.,smaller pore sizes result in smaller energy input requirement).Conventional chalcogenide memory cell fabrication techniques provide aminimum lateral pore dimension, diameter or width of the pore, that islimited by the photolithographic size limit. This results in pore sizeshaving minimum lateral dimensions down to approximately 0.35 micron.

The present invention is directed to overcoming, or at least reducingthe affects of, one or more of the problems set forth above. Inparticular, the present invention provides a method for fabricatingelectrodes for chalcogenide memory cells with minimum lateral dimensionsbelow the photolithographic limit thereby reducing the required energyinput to the chalcogenide active region in operation. The ultra-smallelectrodes are further selected to provide material properties whichpermit enhanced control of the current passing through the chalcogenidememory cell. As a result, the memory cells may be made smaller toprovide denser memory arrays, and the overall power requirements for thememory cell are minimized.

DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thefollowing detailed description of the preferred embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a fragmentary cross sectional view of the deposition of alayer of tetraethylorthosilicate (TEOS) oxide onto a substrate oftitanium nitride in accordance with a first preferred embodiment of thepresent invention;

FIG. 2 is a fragmentary cross sectional view of the formation of anopening in the layer of TEOS oxide of FIG. 1;

FIG. 2 a is an overhead view of a generally rectangular opening formedin the layer of TEOS oxide of FIG. 1;

FIG. 2 b is an overhead view of a generally circular opening formed inthe layer of TEOS oxide of FIG. 1;

FIG. 3 is a fragmentary cross sectional view of the deposition of alayer of silicon nitride onto the layer of TEOS oxide and into theopening in the layer of TEOS oxide of FIG. 2;

FIG. 4 is a fragmentary cross sectional view of the deposition of alayer of polysilicon onto the layer of silicon nitride and opening ofFIG. 3;

FIG. 5 is a fragmentary cross sectional view of the etching of the layerof polysilicon of FIG. 4 to form a spacer;

FIG. 6 is a fragmentary cross sectional view of the etching of theexposed portion of the layer of silicon nitride circumscribed by thespacer of FIG. 5 to form an opening in the layer of silicon nitride;

FIG. 7 is a fragmentary cross sectional view of the removal of thespacer of FIG. 6;

FIG. 8 is a fragmentary cross sectional view of the thin-film depositionof a layer of chalcogenide material into the pore of FIG. 7;

FIG. 9 is a fragmentary cross sectional view of the apparatus of FIG. 8following a chemical mechanical polishing (CMP) operation tosubstantially level the layers of material;

FIG. 10 is a fragmentary cross sectional view of the formation of achalcogenide memory cell using the apparatus of FIG. 9 illustrating theaddition of an upper electrode material layer, an insulating layer, anupper conductive grid layer, and an overlying insulating oxide layer;

FIG. 11 is a fragmentary cross sectional view of the deposition oflayers of silicon nitride and polysilicon onto a substrate of titaniumnitride in accordance with a second preferred embodiment of the presentinvention;

FIG. 12 is a fragmentary cross sectional view of the formation of anopening in the layer of polysilicon and a recess in the layer of siliconnitride of FIG. 11;

FIG. 13 is a fragmentary cross sectional view of the deposition of asecond layer of polysilicon onto the first layer of polysilicon and intothe opening in the layer of polysilicon and into the recess in the layerof silicon nitride of FIG. 12;

FIG. 14 is a fragmentary cross sectional view of the etching of thesecond layer of polysilicon of FIG. 13 to form a spacer;

FIG. 15 is a fragmentary cross sectional view of the etching of theportions of the layer of silicon nitride circumscribed by the spacer ofFIG. 14 to form an opening in the layer of silicon nitride;

FIG. 16 is a fragmentary cross sectional view of the removal of thespacer and layer of polysilicon of FIG. 15;

FIG. 17 is a fragmentary cross sectional view of the thin-filmdeposition of a layer of chalcogenide material into the pore of FIG. 16;

FIG. 18 is a fragmentary cross sectional view of the apparatus of FIG.17 following a chemical mechanical polishing (CMP) operation tosubstantially level the layers of material;

FIG. 19 is a fragmentary cross sectional view of the formation of achalcogenide memory cell using the apparatus of FIG. 18 illustrating theaddition of an upper electrode material layer, an insulating layer, anupper conductive grid layer, and an overlying insulating oxide layer;

FIG. 20 is a fragmentary cross sectional view of the deposition oflayers of silicon nitride, silicon dioxide, and polysilicon onto asubstrate of titanium nitride in accordance with a third preferredembodiment of the present invention;

FIG. 21 is a fragmentary cross sectional view of the formation of anopening in the layer of polysilicon of FIG. 20;

FIG. 22 is a fragmentary cross sectional view of the deposition of asecond layer of polysilicon onto the first layer of polysilicon and intothe opening in the first layer of polysilicon of FIG. 21;

FIG. 23 is a fragmentary cross sectional view of the etching of thesecond layer of polysilicon of FIG. 22 to form a spacer;

FIG. 24 is a fragmentary cross sectional view of the etching of theportions of the layers of silicon nitride and silicon dioxidecircumscribed by the spacer of FIG. 21 to form an opening in the layersof silicon nitride and silicon dioxide;

FIG. 25 is a fragmentary cross sectional view of the removal of thespacer and layers of silicon dioxide and polysilicon of FIG. 24;

FIG. 26 is a fragmentary cross sectional view of the removal of thelayer of silicon dioxide of FIG. 25;

FIG. 27 is a fragmentary cross sectional view of the thin-filmdeposition of a layer of chalcogenide material into the pore of FIG. 26;

FIG. 28 is a fragmentary cross sectional view of the apparatus of FIG.27 following a chemical mechanical polishing (CMP) operation tosubstantially level the layers of material; and

FIG. 29 is a fragmentary cross sectional view of the formation of achalcogenide memory cell using the apparatus of FIG. 28 illustrating theaddition of an upper electrode material layer, an insulating layer, anupper conductive grid layer, and an overlying insulating oxide layer.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

A method of fabricating ultra-small electrodes for chalcogenide memoriesis presented that provides electrode sizes smaller than that presentlyprovided using conventional photolithographic methods. In particular,the preferred embodiment of the present invention provides a method offabricating electrodes for chalcogenide memories that relies upondisposable spacers to define the minimum lateral dimension of a poreinto which the electrode is positioned. In this manner, electrodeshaving minimum lateral dimensions as small as around 500 Angstroms areobtained. The present preferred embodiment further provides enhancedcontrol of the current passing through the resulting chalcogenide memoryby use of metal organic materials as the selected material for theultra-small electrodes.

Turning to the drawings and referring initially to FIGS. 1 to 10, afirst preferred embodiment of a method for fabricating ultra-smallelectrodes for chalcogenide memories will now be described. A layer 10of tetraethylorthosilicate (TEOS) oxide is first deposited onto asubstrate 20 of titanium nitride using convention thin film depositiontechniques as shown in FIG. 1. The layer 10 may have a substantiallyuniform thickness ranging from about 200 to 5000 Angstroms, andpreferably it will have a substantially uniform thickness ofapproximately 200 Angstroms. The layer 10 may be comprised of TEOS oxideor plasma enhanced chemical vapor deposition (PECVD) of SiO₂, andpreferably will be comprised of TEOS oxide. The substrate 20 may becomprised of a conductive material such as, for example, TiN, Carbon,WiSi_(x), or Tungsten, and preferably will be comprised of TiN. Thesubstrate will further preferably comprise a lower electrode grid usedfor accessing an array of chalcogenide memories.

An opening 30, extending to the layer 20, is then etched in the layer 10using conventional anisotropic etching and masking techniques as shownin FIG. 2. The opening 30 may be formed, for example, as a generallyrectangular channel as shown in FIG. 2 a, or as a substantially circularopening in the layer 10 as shown in FIG. 2 b. The opening 30 ispreferably formed using a conventional contact hole mask resulting inthe substantially circular opening shown in FIG. 2 b. The minimumlateral dimension x₁ of the opening 30 may range from about 2500 to 8000Angstroms, and preferably it will be approximately 5000 Angstroms. Theopening 30 includes a generally horizontal bottom surface 40, common tothe layer 20, and generally vertical side walls 50 at its outerperiphery.

A layer 80 of silicon nitride is then deposited onto the layer 10 andbottom surface 40 using conventional thin film deposition techniques asshown in FIG. 3. The portion of the layer 80 positioned within theopening 30 includes generally vertical side walls 82 extending downwardto a generally horizontal surface 84. The layer 80 may have asubstantially uniform thickness ranging from about 100 to 750 Angstroms,and preferably it will have a substantially uniform thickness ofapproximately 300 Angstroms. The layer 80 may comprise a dielectricmaterial such as, for example, TEOS oxide, PECVD oxide, or siliconnitride, and preferably it will comprise silicon nitride.

A layer 90 of polysilicon is then deposited onto the layer 80 usingconventional thin film deposition techniques as shown in FIG. 4. Thelayer 90 may have a substantially uniform thickness ranging from about500 to 2500 Angstroms, and preferably it will have a substantiallyuniform thickness of approximately 1500 Angstroms. The layer 90 maycomprise polysilicon or silicon nitride, and preferably it will comprisepolysilicon. The layer 90 is then etched using conventional anisotropicetching techniques to form a spacer 100 out of the layer 90 as shown inFIG. 5. The spacer 100 is positioned at the outer periphery of theportion of the layer 80 positioned within the opening 30 and covers thegenerally vertical side walls 82. The bottom of the spacer 100 will havea lateral thickness substantially equal to the selected thickness of thelayer 90 provided the coating of the layer 90 on the layer 80 isconformal.

The portion of the layer 80 not covered by the spacer 100 is then etchedusing conventional anisotropic etching techniques to form an opening 110defining a pore in the layer 80 extending to the layer 20 as shown inFIG. 6. The resulting opening 110 may have a minimum lateral dimensionranging from about 500 to 4000 Angstroms, and preferably it will have aminimum lateral dimension of approximately 1000 Angstroms. The minimumlateral dimension of the opening 110 is defined by the selectedthickness of the layer 90 used to form the spacer 100. The spacer 100 isthen removed using conventional wet etch techniques as shown in FIG. 7.The disposable spacer 100 thus provides a means of defining the minimumlateral dimension of an ultra-small pore in the layer 80. The firstpreferred embodiment of the present method thus provides a means offabricating an ultra-small pore 110 in the layer 80 by use of thedisposable spacer 100 positioned adjacent to an edge feature of thelayer 80.

Note that while a range of materials may be utilized for each of thelayers, the particular materials selected for each of the layers must beselected to provide proper selectivity during the various etchingprocesses as will be recognized by persons of ordinary skill in the art.

The resulting structure illustrated in FIG. 7 includes a conductivesubstrate 20 and a dielectric layer 80 including an opening 110. Thisstructure is then preferably used to fabricate a chalcogenide memorycell in which the opening 110 provides a pore for placement of anelectrode for the chalcogenide memory cell. The chalcogenide memory cellis fabricated by first depositing a layer 120 of a metal organic (MO)material such as, for example, Ti, TiN, or TiC_(x)N_(y) usingconventional thin film deposition methods such as, for example, chemicalvapor deposition (CVD) as illustrated in FIG. 8. In a preferredembodiment, the MO material comprises TiC_(x)N_(y). The MOCVD materiallayer fills the pore 110 and thereby providing an ultra-small electrodefor use in the chalcogenide memory cell. The resulting structure is thenpreferably substantially planarized using a conventional chemicalmechanical planarization (CMP) process as illustrated in FIG. 9.

The chalcogenide memory cell 130 is then formed incorporating theultra-small electrode 120 using conventional semiconductor processingprocesses such as, for example, thin-film deposition, masking, andetching processes. The chalcogenide memory cell 130 preferably includesa layer 140 of a chalcogenide material, a layer 150 of a conductivematerial serving as an upper electrode, an insulative layer 160, anupper conductive layer 170, and an overlying insulative oxide layer 180.

The chalcogenide material layer 140 may be deposited using conventionalthin film deposition methods. The chalcogenide material layer may rangefrom approximately 100 to 2000 Angstroms, and preferably it is around1000 Angstroms thick. Typical chalcogenide compositions for these memorycells 130 include average concentrations of Te in the amorphous statewell below 70%, typically below about 60% and ranging in general from aslow as about 23% up to about 56% Te, and most preferably to about 48% to56% Te. Concentrations of Ge are typically above about 15% and rangefrom a low of about 17% to about 44% average, remaining generally below50% Ge, with the remainder of the principal constituent elements in thisclass being Sb. The percentages given are atomic percentages which total100% of the atoms of the constituent elements. In a particularlypreferred embodiment, the chalcogenide compositions for these memorycells comprise a Te concentration of about 55%, a Ge concentration ofabout 22%, and a Sb concentration of about 22%. This class of materialsare typically characterized as Te_(a)Ge_(b)Sb_(100-(a+b)), where a isequal to or less than about 70% and preferably between about 60% toabout 40%, b is above about 15% and less than 50%, preferably betweenabout 17% to about 44%, and the remainder is Sb.

The layer 150 of conductive material may comprise materials such as, forexample, titanium nitride which is deposited over the chalcogenide layer140 using conventional thin film deposition techniques. The layer 150thereby provides an upper electrode for the chalcogenide memory cell130. The layer 150 may have a thickness ranging from approximately 100to 2000 Angstroms, and preferably it has a thickness of around 600Angstroms. The layer 150 may comprise a conductive material such as, forexample, TiN or Carbon, and preferably it will comprise TiN. The layers140 and 150 are subsequently etched back using conventional masking andetching processes. The insulating layer 160 is then applied usingconventional thin film PECVD deposition processes. The insulating layer160 may range in thickness from approximately 100 to 5000 Angstroms, andpreferably it has a thickness of around 500 Angstroms. The insulatinglayer 160 may comprise Si₃N₄, SiO₂, or TEOS, and preferably it willcomprise Si₃N₄. The overlying oxide layer 180 is then applied usingconventional processes such as, for example, TEOS. The insulating layer160 and the overlying oxide layer 180 are then etched back usingconventional masking and etching processes to provide access to theconductive layer or electrode 150 by the upper conductive grid 170. Theupper conductive grid material 170 may be applied using conventionalthin-film deposition processes. The upper conductive grid material 170may comprise materials such as, for example, aluminum alloy, TiW, or CVDW over TiN, and preferably it will comprise Al/Cu. In an alternativeembodiment, layer 160 is applied using TEOS, ranging in thickness fromapproximately 500 to 5000 Angstroms, preferably with a thickness ofapproximately 3500 Angstroms, and layer 180 is eliminated.

In a particularly preferred embodiment, the methods described areutilized to form an array of chalcogenide memory cells 130 which areaddressable by an X-Y grid of upper and lower conductors. In theparticularly preferred embodiment, diodes are further provided in serieswith the chalcogenide memories in order to permit read/write operationsfrom/to individual chalcogenide memory cells as will be recognized bypersons of ordinary skill in the art.

Referring to FIGS. 11 to 19, a second preferred embodiment of a methodof fabricating ultra-small electrodes for chalcogenide memory cells willnow be described. A layer 210 of silicon nitride is first deposited ontoa substrate 220 of titanium nitride. A layer 230 of polysilicon is thendeposited onto the layer 210. The layers 210 and 230 are deposited usingconventional thin film deposition techniques as shown in FIG. 11. Thelayer 210 may have a substantially uniform thickness ranging from about50 to 1000 Angstroms, and preferably it will have a substantiallyuniform thickness of approximately 500 Angstroms. The layer 210 may becomprised of an insulating material such as, for example, TEOS oxide,silicon nitride, or PECVD oxide, and preferably will be comprised ofsilicon nitride. The layer 230 may have a substantially uniformthickness ranging from about 1000 to 5000 Angstroms, and preferably itwill have a substantially uniform thickness of approximately 4000Angstroms. The layer 230 may be comprised of TEOS oxide, PECVD oxide, orpolysilicon, and preferably will be comprised of polysilicon. Thesubstrate 220 may be comprised of a conductive material such as, forexample, TiN, carbon, WSi, or TiW, and preferably will be comprised ofTiN. In a preferred embodiment, the substrate 220 will comprise aconductive lower grid for accessing an array of chalcogenide memorycells.

An opening 240, extending partially into the layer 210, is then etchedin the layers 210 and 230 using conventional anisotropic etching andmasking techniques as shown in FIG. 12. The etching process may etchmaterial partially from the layer 210 thereby forming a recess in thelayer 210. The opening 240 may be formed, for example, as a rectangularchannel or as a substantially circular opening in the layers 210 and230. The opening 240 is preferably formed using a conventional circularcontact hole mask resulting in a substantially circular opening. Theminimum lateral dimension Y₁ of the opening 240 may range from about2500 to 8000 Angstroms, and preferably it will be approximately 5000Angstroms. The opening 240 includes a generally horizontal bottomsurface 250 and generally vertical side walls 260 at its outerperiphery.

A second layer 270 of polysilicon is then deposited onto the layer 230and into the opening 240, onto the bottom surface 250 and side walls260, using conventional thin film deposition techniques as shown in FIG.13. The layer 270 may have a substantially uniform thickness rangingfrom about 500 to 3500 Angstroms, and preferably it will have asubstantially uniform thickness of approximately 2000 Angstroms. Thelayer 270 may comprise polysilicon, TEOS oxide, or PECVD oxide, andpreferably it will comprise polysilicon. The layer 270 is then etchedusing conventional anisotropic etching techniques to form a spacer 280out of the layer 270 as shown in FIG. 14. The spacer 280 is positionedat the outer periphery of the opening 240 and covers the generallyvertical side walls 260. The bottom of the spacer 280 will have alateral thickness substantially equal to the selected thickness of thelayer 270 provided the layer 270 conformally coats the layers 210 and230.

The portion of the layer 210 not covered by the spacer 280 are thenetched using conventional anisotropic etching techniques to form anopening 290 defining a pore in the layer 210 extending to the layer 220as shown in FIG. 15. The resulting opening 290 may have a minimumlateral dimension ranging from about 500 to 4000 Angstroms, andpreferably it will have a minimum lateral dimension of approximately1000 Angstroms. The minimum lateral dimension of the opening 290 isdefined by the selected thickness of the layer 270 used in forming thespacer 280. The spacer 280 and layer 230 are then removed usingconventional etching techniques as shown in FIG. 16. The disposablespacer 280 thus provides a means of defining the minimum lateraldimension of an ultra-small pore in the layer 210. The second preferredembodiment of the present method thus provides a means of fabricating anultra-small pore 290 in the layer 210 by use of a disposable spacer 280positioned adjacent to an edge feature of the layer 230.

Note that while a range of materials may be utilized for each of thelayers, the particular materials selected for each of the layers must beselected to provide proper selectivity during the various etchingprocesses as will be recognized by persons of ordinary skill in the art.

The resulting structure illustrated in FIG. 16 includes a conductivesubstrate 220 and an insulating layer 210 including the opening 290surrounded by a recess 300. The resulting structure illustrated in FIG.16 including the opening 290 may also be provided, without the recess300 in the layer 210, where the etch selectivities of the previousprocesses avoid etching the recess 300 in the layer 210. This structureis then preferably used to fabricate a chalcogenide memory cell in whichthe opening 290 provides a pore for placement of an electrode for thechalcogenide memory cell. The chalcogenide memory cell is fabricated byfirst depositing a layer 310 of a metal organic (MO) material such as,for example, Ti, TiN, or TiC_(x)N_(y) using conventional thin filmdeposition methods such as, for example, chemical vapor deposition (CVD)as illustrated in FIG. 17. In a preferred embodiment, the MO materialcomprises TiC_(x)N_(y). The MOCVD material layer fills the pore 290 andthereby providing an ultra-small electrode for use in the chalcogenidememory cell. The resulting structure is then preferably substantiallyplanarized using a conventional chemical mechanical planarization (CMP)process as illustrated in FIG. 18.

The chalcogenide memory cell 320 is then formed incorporating theultra-small electrode 310 using conventional semiconductor processingprocesses such as, for example, thin-film deposition, masking, andetching processes. The chalcogenide memory cell 310 preferably includesa layer 340 of a chalcogenide material, a layer 350 of a conductivematerial serving as an upper electrode, an insulative layer 360, anupper conductive layer 370, and an overlying insulative oxide layer 380.

The chalcogenide material layer 340 may be deposited using conventionalthin film deposition methods and may have a thickness ranging fromapproximately 100 to 2000 Angstroms, and preferably it has a thicknessof about 1000 Angstroms. Typical chalcogenide compositions for thesememory cells 320 include average concentrations of Te in the amorphousstate well below 70%, typically below about 60% and ranging in generalfrom as low as about 23% up to about 56% Te, and most preferably toabout 48% to 56% Te. Concentrations of Ge are typically above about 15%and range from a low of about 17% to about 44% average, remaininggenerally below 50% Ge, with the remainder of the principal constituentelements in this class being Sb. The percentages given are atomicpercentages which total 100% of the atoms of the constituent elements.In a particularly preferred embodiment, the chalcogenide compositionsfor these memory cells comprise a Te concentration of about 55%, a Geconcentration of about 22%, and a Sb concentration of about 22%. Thisclass of materials are typically characterized asTe_(a)Ge_(b)Sb_(100-(a+b)), where a is equal to or less than about 70%and preferably between about 60% to about 40%, b is above about 15% andless than 50%, preferably between about 17% to about 44%, and theremainder is Sb.

The layer 350 of conductive material may comprise materials such as, forexample, titanium nitride which is deposited over the chalcogenide layer340 using conventional thin film deposition techniques. The layer 350thereby provides an upper electrode for the chalcogenide memory cell320. The layer 350 may range in thickness from approximately 100 to 2000Angstroms, and preferably it has a thickness of about 600 Angstroms. Thelayer 350 may comprise a conductive material such as, for example, TiNor Carbon, and preferably it will comprise TiN. The layers 340 and 350are subsequently etched back using conventional masking and etchingprocesses. The insulating layer 360 is then applied using conventionalthin film PECVD deposition processes. The insulating layer 360 maycomprise Si₃N₄, SiO₂, or TEOS, and preferably it will comprise Si₃N₄.The insulating layer 360 may range in thickness from approximately 100to 5000 Angstroms, and preferably it has a thickness of around 500Angstroms The overlying oxide layer 380 is then applied usingconventional processes such as, for example, TEOS. The insulating layer360 and the overlying oxide layer 380 are then etched back usingconventional masking and etching processes to provide access to theconductive layer or electrode 350 by the upper conductive grid 370. Theupper conductive grid material 370 may be applied using conventionalthin-film deposition processes. The upper conductive grid material 370may comprise materials such as, for example, aluminum alloy, TiW, or CVDW over TiN, and preferably it will comprise Al/Cu. In an alternativeembodiment, layer 360 is applied using TEOS, ranging in thickness fromapproximately 500 to 5000 Angstroms, preferably with a thickness ofapproximately 3500 Angstroms, and layer 380 is eliminated.

In a particularly preferred embodiment, the methods described areutilized to form an array of chalcogenide memory cells 320 which areaddressable by an X-Y grid of upper and lower conductors. In theparticularly preferred embodiment, diodes are further provided in serieswith the chalcogenide memories in order to permit read/write operationsfrom/to individual chalcogenide memory cells as will be recognized bypersons of ordinary skill in the art.

Referring to FIGS. 20 to 29, a third preferred embodiment of a method offabricating ultra-small pores will now be described. A layer 410 ofsilicon nitride is first deposited onto a substrate 420 of titaniumnitride. Layers 430 of silicon dioxide and 440 of polysilicon are thensuccessively deposited onto the layer 410. In an alternative embodiment,layer 430 is not deposited. The layers 410, 430, and 440 are depositedusing conventional thin film deposition techniques as shown in FIG. 20.The layer 410 may have a substantially uniform thickness ranging fromabout 100 to 1000 Angstroms, and preferably it will have a substantiallyuniform thickness of approximately 500 Angstroms. The layer 410 may becomprised of a dielectric material such as, for example, siliconnitride, TEOS oxide, or PECVD oxide, and preferably it will be comprisedof silicon nitride. The layer 430 may have a substantially uniformthickness ranging from about 100 to 1500 Angstroms, and preferably itwill have a substantially uniform thickness of approximately 700Angstroms. The layer 430 may be comprised of TEOS oxide or PECVD oxide,and preferably it will be comprised of TEOS oxide. The layer 440 mayhave a substantially uniform thickness ranging from about 2000 to 5000Angstroms, and preferably it will have a substantially uniform thicknessof approximately 4000 Angstroms. The layer 440 may be comprised ofpolysilicon, TEOS oxide, or PECVD oxide, and preferably will becomprised of polysilicon. The substrate 420 may be comprised of aconductive material such as, for example, TiN, carbon, WSi_(x), or TiW,and preferably will be comprised of TiN. In a preferred embodiment, thesubstrate layer 420 will comprise a conductive lower grid for accessingan array of chalcogenide memory cells.

An opening 450, extending downward to the layer 430, is then etched inthe layer 440 using conventional anisotropic etching and maskingtechniques as shown in FIG. 21. The composition of the layer 430 isselected to prevent any material within the layer 410 from being etchedaway by this process. The opening 450 may be formed, for example, as arectangular channel or as a substantially circular opening in the layer440. The opening 450 is preferably formed using a conventional contacthole mask resulting in a substantially circular opening. The minimumlateral dimension z₁ of the opening 450 may range from about 2500 to8000 Angstroms, and preferably it will be approximately 5000 Angstroms.The opening 450 includes a generally horizontal bottom surface 460 andgenerally vertical side walls 470 at its outer periphery.

A second layer 480 of polysilicon is then deposited onto the layer 440and into the opening 450, onto the bottom surface 460 and side walls470, using conventional thin film deposition techniques as shown in FIG.22. The layer 480 may have a substantially uniform thickness rangingfrom about 500 to 3500 Angstroms, and preferably it will have asubstantially uniform thickness of approximately 2000 Angstroms. Thelayer 480 may comprise polysilicon, TEOS oxide, or PECVD oxide, andpreferably it will comprise polysilicon. The layer 480 is then etchedusing conventional anisotropic etching techniques to form a spacer 490out of the layer 480 as shown in FIG. 23. The spacer 490 is positionedat the outer periphery of the opening 450 and covers the generallyvertical side walls 470. The bottom of the spacer 490 will have alateral thickness substantially equal to the selected thickness of thelayer 480 provided that the layer 480 conformally coats the layer 440.

The portions of the layers 410 and 430 not covered by the spacer 490 arethen etched using conventional anisotropic etching techniques to form anopening 500 defining a pore in the layers 410 and 430 extending to thelayer 420 as shown in FIG. 24. The resulting opening 500 may have aminimum lateral dimension ranging from about 500 to 4000 Angstroms, andpreferably it will have a minimum lateral dimension of approximately1000 Angstroms. The minimum lateral dimension of the opening 500 isdefined by the selected thickness of the layer 480. The spacer 490,layer 440, and layer 430 are then removed using conventional etchingtechniques as shown in FIGS. 25 and 26. The disposable spacer 490 thusprovides a means of defining an ultra-small pore in the layers 410 and430. The third preferred embodiment of the present method thus providesa means of fabricating an ultra-small pore 500 in the layers 410 and 430by use of the disposable spacer 490 positioned adjacent to an edgefeature of the layer 440.

Note that while a range of materials may be utilized for each of thelayers, the particular materials selected for each of the layers must beselected to provide proper selectivity during the various etchingprocesses.

The resulting structure illustrated in FIG. 26 includes a conductivesubstrate 420 and a dielectric layer 410 including the opening 500. Thisstructure is then preferably used to fabricate a chalcogenide memorycell in which the opening 500 provides a pore for placement of anelectrode for the chalcogenide memory cell. The chalcogenide memory cellis fabricated by first depositing a layer 510 of a metal organic (MO)material such as, for example, Ti, TiN, or TiC_(x)N_(y) usingconventional thin film deposition methods such as, for example, chemicalvapor deposition (CVD) as illustrated in FIG. 27. In a preferredembodiment, the MO material comprises TiC_(x)N_(y). The MOCVD materiallayer fills the pore 500 and thereby provides an ultra-small electrodefor use in the chalcogenide memory cell. The resulting structure is thenpreferably substantially planarized using a conventional chemicalmechanical planarization (CMP) process as illustrated in FIG. 28.

The chalcogenide memory cell 520 is then formed incorporating theultra-small electrode 510 using conventional semiconductor processingprocesses such as, for example, thin-film deposition, masking, andetching processes. The chalcogenide memory cell 520 preferably includesa layer 530 of a chalcogenide material, a layer 540 of a conductivematerial serving as an upper electrode, an insulative layer 550, anupper conductive layer 560, and an overlying insulative oxide layer 570.

The chalcogenide material layer 530 may be deposited using conventionalthin film deposition methods. The chalcogenide material layer 530 mayrange in thickness from approximately 100 to 2000 Angstroms, andpreferably it has a thickness of around 1000 Angstroms. Typicalchalcogenide compositions for these memory cells 520 include averageconcentrations of Te in the amorphous state well below 70%, typicallybelow about 60% and ranging in general from as low as about 23% up toabout 56% Te, and most preferably to about 48% to 56% Te. Concentrationsof Ge are typically above about 15% and range from a low of about 17% toabout 44% average, remaining generally below 50% Ge, with the remainderof the principal constituent elements in this class being Sb. Thepercentages given are atomic percentages which total 100% of the atomsof the constituent elements. In a particularly preferred embodiment, thechalcogenide compositions for these memory cells comprise a Teconcentration of about 55%, a Ge concentration of about 22%, and a Sbconcentration of about 22%. This class of materials are typicallycharacterized as Te_(a)Ge_(b)Sb_(100-(a+b)), where a is equal to or lessthan about 70% and preferably between about 60% to about 40%, b is aboveabout 15% and less than 50%, preferably between about 17% to about 44%,and the remainder is Sb.

The layer 540 of conductive material may comprise materials such as, forexample, titanium nitride which is deposited over the chalcogenide layer530 using conventional thin film deposition techniques. The layer 540thereby provides an upper electrode for the chalcogenide memory cell520. The layer 540 may range in thickness from approximately 100 to 2000Angstroms, and preferably it has a thickness of around 600 Angstroms.The layer 540 may comprise a conductive material such as, for example,TiN or Carbon, and preferably it will comprise TiN. The layers 530 and540 are subsequently etched back using conventional masking and etchingprocesses. The insulating layer 550 is then applied using conventionalthin film PECVD deposition processes. The insulating layer 550 maycomprise Si₃N₄, SiO₂, or TEOS, and preferably it will comprise Si₃N₄.The insulating layer 550 may range in thickness from approximately 100to 5000 Angstroms, and preferably it has a thickness of around 500Angstroms. The overlying oxide layer 570 is then applied usingconventional processes such as, for example, TEOS. The insulating layer550 and the overlying oxide layer 570 are then etched back usingconventional masking and etching processes to provide access to theconductive layer or electrode 540 by the upper conductive grid 560. Theupper conductive grid material 560 may be applied using conventionalthin-film deposition processes. The upper conductive grid material 560may comprise materials such as, for example, aluminum alloy, TiW, or CVDW over TiN, and preferably it will comprise Al/Cu. In an alternativeembodiment, layer 550 is applied using TEOS, ranging in thickness fromapproximately 500 to 5000 Angstroms, preferably with a thickness ofapproximately 3500 Angstroms, and layer 570 is eliminated.

In a particularly preferred embodiment, the methods described areutilized to form an array of chalcogenide memory cells 520 which areaddressable by an X-Y grid of upper and lower conductive grids. In theparticularly preferred embodiment, diodes are further provided in serieswith each of the chalcogenide memories in order to permit read/writeoperations from/to individual chalcogenide memory cells as will berecognized by persons of ordinary skill in the art.

A method has been described for forming ultra-small electrodes for usein chalcogenide memory cells using disposable internal spacers. Moregenerally, the present method will also provide ultra-small plugcontacts or vias in semiconductor devices such as, for example, staticrandom access and dynamic random access memories. Such semiconductordevices require contacts to permit electrical connection to activeregions of memory elements. The present method of forming will alsoprovide ultra-small contacts or vias in semiconductor devices generallythereby permitting further reduction in the physical size of suchdevices.

While the invention is susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

1. A method of fabricating a phase change memory cell, comprising:applying a first layer of material onto a substrate; removing a portionof the first layer to form an opening in the first layer to thesubstrate; applying a second layer of material over the opening in thefirst layer; applying a third layer of material over the second layer;removing a portion of the second and third layer of material to form anopening through the second layer of material to the substrate, whereinthe opening through the second layer is smaller than the opening in thefirst layer of material; removing the remainder of the third layer;applying a fourth layer of material over the opening in the secondlayer; removing a portion of the second layer and the fourth layer; andapplying a layer of phase change memory material over a remainingportion of the fourth layer disposed within the opening through thesecond layer.
 2. The method of claim 1, wherein the phase change memorymaterial includes a chalcogenide memory material.
 3. The method of claim1, wherein the first layer of material comprises TEOS.
 4. The method ofclaim 1, wherein the second layer of material comprises silicon nitride.5. The method of claim 1, wherein the third layer of material comprisespolysilicon.
 6. The method of claim 1, wherein the fourth layer ofmaterial comprises a metal organic material.
 7. A method of fabricatinga phase change memory cell, comprising: applying a first layer ofmaterial onto a substrate; applying a second layer of material onto thefirst layer; removing a portion of the second layer to form an openingthrough the second layer to the first layer; applying a third layer ofmaterial over the opening through the second layer to the first layer;removing a portion of the third layer to form an opening through thethird layer to the first layer; removing a portion of the first layer toform an opening through the first layer to the substrate; applying afourth layer of material over the opening through the first layer to thesubstrate; removing a portion of the fourth layer; and applying a layerof phase change memory material over a remaining portion of the fourthlayer disposed within the opening through the first layer to thesubstrate.
 8. The method of claim 7, wherein the opening created byremoval of the portion of the second layer is wider than the openingcreated by removal of the portion of the third layer.
 9. The methodclaim 7, wherein the opening formed by the removal of the portion of thefirst layer is equal in width to the opening formed by removal of theportion of the third layer.
 10. The method of claim 7, wherein the firstlayer has a substantially uniform thickness of approximately 500angstroms.
 11. The method of claim 7, wherein the second layer has asubstantially uniform thickness of approximately 4000 angstroms.
 12. Themethod of claim 7, wherein the opening formed in the second layer iscircular in cross-section.
 13. The method of claim 12, wherein thecircular opening has an approximate diameter of 5000 angstroms.
 14. Themethod of claim 7, wherein the opening formed in the third layer issubstantially circular.
 15. The method of claim 14, wherein the circularopening formed in the third layer has an approximate diameter of 1000angstroms.
 16. A method of fabricating a phase change memory cell,comprising: applying a first layer of material onto a substrate;applying a second layer of material onto the first layer; removing aportion of the second layer to form an opening through the second layerto the first layer; applying a third layer of material over the openingthrough the second layer to the first layer; removing a portion of thethird layer to form an opening through the third layer to the firstlayer; removing a portion of the first layer to form an opening throughthe first layer to the substrate; removing the remainder of the thirdlayer and the second layer; applying a fourth layer over the openingthrough the first layer; removing a portion of the fourth layer; andapplying a layer of phase change material over a remaining portion ofthe fourth layer disposed within the opening through the first layer.17. The method of claim 16, wherein the opening formed in the secondlayer is rectangular in cross-section perpendicular to the normal of thesubstrate.
 18. The method of claim 17, wherein the width of therectangular opening is approximately 5000 angstroms.
 19. The method ofclaim 16, wherein the opening in the third layer is rectangular incross-section perpendicular to the normal of the substrate.
 20. Themethod of claim 19, wherein the width of the rectangular opening in thethird layer is approximately 1000 angstroms.